Downstream time domian based adaptive modulation for DOCSIS based applications

ABSTRACT

In a DOCSIS based satellite gateway data is transmitted over a single downstream channel, at different throughput rates. Data destined for each subscriber/receiver is assigned a throughput rate depending upon the downstream signal quality of that subscriber/receiver. To accomplish this, the downstream DOCSIS MAC data is parsed to extract DOCSIS packets. The DOCSIS packets are then loaded into packet queues based on an identifier within such packets such as the MAC destination address or SID. Each of the queues represents a bandwidth efficiency or throughput rate that can be currently tolerated by specific subscribers based on the current signal quality being experienced at the subscriber location. A PHY-MAP describing the downstream data structure to be transmitted and inserted into the downstream data. Data is extracted from the packet queues in queue blocks as defined by the PHY-MAP. The queue blocks are modulated with transmission parameters appropriate for each queue block and transmitted to the DOCSIS based satellite modems. The satellite modems extract the PHY-MAP from the downstream data and use the information contained in it to demodulate and decode the queue for which they have sufficient downstream signal quality. Satellite modems measure and transmit downstream signal quality to the satellite gateway to be used to assigned traffic to the appropriate queues.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional ApplicationSerial No. 60/424,205, filed Nov. 6, 2002, which is incorporated hereinby reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to broadband communication systems, andmore particularly those that use the Data Over Cable Service InterfaceSpecification (DOCSIS) media access protocol or its derivatives.

[0004] 2. Description of the Related Art

[0005] Communication systems are known to support wireless and wirelined communications between wireless and/or wire lined communicationdevices. Such communication systems range from national and/orinternational cellular telephone systems, to the Internet, to cablesystems, to local area networks (LANs), to wide area networks (WANs) toin-home wireless networks and the like. Often, these systems arecomprised of numerous different forms of transmission media.

[0006] In the example of two-way data communications via satellite, datamay be transmitted using time division multiplexing (TDM) over a singlecarrier (i.e. channel). A gateway receives data from a network such asthe Internet, performs forward error correction (FEC) then modulates thedata. The data is transmitted up to a satellite and back down from thesatellite to one or more receivers.

[0007] For each communication device to participate in communications ofwhatever type, it includes or is coupled to a transceiver (i.e., forterrestrial wireless, a radio receiver and transmitter; and for two-waysatellite, a satellite receiver and transmitter). As is known, thetransmitter of radio and satellite transceivers include a datamodulation stage, one or more intermediate frequency stages, and a poweramplifier. The data modulation stage converts raw data into basebandsignals in accordance with the particular wireless or satellitecommunication standard. The one or more intermediate frequency stagesmix the baseband signals with the signal generated by one or more localoscillators to produce RF signals. The power amplifier amplifies the RFsignals prior to transmission via an antenna or satellite dish.

[0008] As is also known, the receiver of a transceiver is also coupledto the antenna or satellite dish and includes a low noise amplifier, oneor more intermediate frequency stages, a filtering stage, and a datarecovery (i.e. demodulation) stage. The low noise amplifier receives aninbound RF signal via the antenna or satellite dish and amplifies it.The one or more intermediate frequency stages mix the amplified RFsignal with the signal generated by one or more local oscillators toconvert the amplified RF signal into a baseband signal or anintermediate frequency (IF) signal. This is typically referred to asfrequency down-conversion. The filtering stage filters thedown-converted baseband or IF signal to eliminate unwanted out of bandsignals to produce a filtered signal that is only that which fallswithin the bandwidth of the selected channel. Thus, this filter issometimes referred to as a channel select filter. The data recovery ordemodulation stage recovers raw data from the filtered signal inaccordance with the particular wireless or satellite communicationstandard.

[0009] One common data network architecture, specified as the Data OverCable Service Interface Specification) DOCSIS¹, originated with cableoperators interested in deploying high-speed packet-based communicationssystems on cable television systems. These include IP based Internetdata, packet telephony service, video conferencing service, and manyothers. The goal of DOCSIS is to define a data service that will allowtransparent bi-directional transfer of Internet Protocol (IP) trafficbetween a cable system headend or Cable Modem Termination System (CMTS)and customer locations using a cable modem (CM), over an all-coaxial orhybrid-fiber/coax (HFC) cable network.

[0010] The DOCSIS Media Access Control (MAC) sublayer specifies that theCMTS provide a single carrier transmitter for each downstream (i.e. fromhead-end to subscriber) channel. All CMs at subscriber locations listento all frames transmitted on the downstream channel upon which they areregistered and accept those frames where the destinations match the CMitself or CPEs (customer premises equipment). CMs can communicate withother CMs only through the CMTS.

[0011] The upstream channel is thus characterized by many transmitters(CMs) and one receiver (the CMTS). Time in the upstream channel isslotted, providing for Time Division Multiple Access at regulated timeticks. The CMTS provides the time reference and controls the allowedusage for each interval. Intervals may be granted for transmissions byparticular CMs, or for contention by all CMs. CMs may contend to requesttransmission time. To a limited extent, CMs may also contend to transmitactual data. In both cases, collisions can occur and retries are thenused.

[0012] The DOCSIS protocol has been adapted to other types of media,including terrestrial fixed wireless and two way satellite. For theseapplications, as well as the original data over cable service, data istransferred between a central location and many remote subscribers. Theterm for the centrally located equipment for broadband terrestrial fixedwireless systems is a Wireless Access Termination System (WATS). Thesubscriber equipment is called a wireless modem. With respect to two waysatellite, the centrally located equipment is a satellite gateway (SG),while the subscriber equipment is a satellite modem (SM). Those ofaverage skill in the art will recognize that in each of these types ofservice, the DOCSIS architecture is substantially maintained, even ifsome of the implementation details are adapted to the type of media usedfor transmission.

[0013] In standard DOCSIS based systems such as those described above,the downstream transmission is defined to be a time division multiplexed(TDM) signal with a fixed modulation type as well as a fixed forwarderror correction (FEC) coding rate. Thus, by nature the downstreamsignal has a fixed spectral efficiency in bits per second/Hertz[bps/Hz]. Signal parameters such as the modulation type, FEC codingtype, and FEC coding rate determine the minimum signal to noise ratio(SNR) that must be present for the SM to have error-free or quasierror-free operation in a given channel having those parametriclimitations. Thus, there is an inherent trade-off between the values ofreceiver parameters that yield a high level of throughput (e.g.high-order modulation and high FEC code rates) and those values (e.g.low-order modulation and more robust but lower FEC code rates) thatensure that the signal can be reliably received under conditions of lowSNR but with lower throughput.

[0014] In many real world environments, subscribers of such systemsexperience a wide range of path losses and channel degradations. Oneexample is a satellite based system where a downstream spot beambroadcasts to SMs that are located over a wide geographic area. Variousconditions such as localized rainfall, partial obstructions, antennamisalignments, etc. can significantly degrade the signal power levels(and thus SNRs) received by individual subscribers. Those of averageskill in the art will recognize that similar channel degradation may beexperienced for subscribers of terrestrial fixed wireless and even dataover cable, although the causes may be different.

[0015]FIG. 1 illustrates the basic elements of a two-way satellitesystem. A satellite gateway (SG) with a baseband modulator/demodulator100 receives data from a network, such as the Internet. The data isassembled into an appropriate format in accordance with, for example theDOCSIS architecture previously described, and is then provided totransceiver 102. The transceiver performs certain functions necessaryfor transmitting the data using the satellite dish 104, up to thesatellite 106 and down to a plurality of SMs 112 over downstream channel114. The downstream signal is received by the dish 108, processed by thetransceiver 110, and demodulated by SM 112. The SMs 112 transmit data,generated by the customer premise equipment (CPE) (not shown) back tothe SG 100 over the upstream channel 116 uses the format recognized bythe SG 100.

[0016]FIG. 2 is a block diagram illustrating the processing blocks of aknown SG 100 a, along with the processing blocks of the transceiver 102.Data from a network 250, such as the Internet, is transmitted betweenthe network and the gateway DOCSIS MAC 204 a. The data is formatted inaccordance with the DOCSIS protocol. This protocol uses an MPEG formatin the “downstream transmission convergence sublayer” that serves as theinterface between the MAC and physical layer (PHY). MPEG specificationsare publicly available and are incorporated herein by this reference forall purposes.

[0017] The downstream MPEG data stream that is output at 240 a from theMAC 204 a is encoded and modulated using a single type of modulation anda single set of FEC parameters by the fixed encoding and modulationstage 206 a. The modulated and encoded MPEG stream is then up convertedand filtered, and then fed into a high power amplifier by transceiver214. This signal is transmitted continuously in a single frequency band,through a satellite (106, FIG. 1) and received by subscriber SMs (112,FIG. 2).

[0018] The SG 100 a also receives (i.e. at antenna dish 104, FIG. 1) theupstream signal transmitted by subscriber satellite modems SM 112 of thesystem. The signal is filtered and down converted back to baseband atstage 212 using a fixed set of demodulation and decoding parameters atstage 208 a to recover the upstream data stream.

[0019]FIG. 3 is a block diagram illustrating the processing blocks of aknown SM 112 a, along with the processing blocks of the transceiver 110.The SM 112 a receives the signal through dish 108 and down converts thesignal using a fixed set of demodulation and decoding parameters torecover the MPEG stream at processing box 540. The information isprocessed by the local DOCSIS MAC 504 a in conjunction with the hostprocessor 500 a. The data is then passed on to the CPE of the subscriberat line 250.

[0020] Note that the modulation type and the FEC encoding parameters arefixed for all data transmitted by the SG 100 a and received by each SM112 a over the downstream channel of the system of FIGS. 2 and 3.Indeed, to ensure that customers do not experience total loss of serviceunder conditions of low SNR, current DOCSIS based systems must operatewith channel parameters (and therefore fixed modulation and FEC encodingparameters) that ensure that even the subscriber situated the worst interms of signal degradation (as manifested by bit error rate or SNR) isable to obtain service with a high probability of success. As a result,the majority of subscribers that could otherwise receive data at ahigher rate are penalized by the presence of the relatively fewerenvironmentally disadvantaged subscribers.

BRIEF SUMMARY OF THE INVENTION

[0021] Thus, in order to overcome the above-described limitations of theprior devices, among other limitations, a satellite communication systemconstructed according to the present invention implements downstreamadaptive modulation that allows subscribers receiving the downstreamchannel with a higher SNR and/or operating in less degraded channels toachieve higher bandwidth efficiency. This results in a combination ofimproved channel capacity, increased throughput, and improved coverage.

[0022] An embodiment of the method of the invention independently andadaptively controls the throughput rate of data traffic destined foreach of a plurality of receivers. First, a number of packet queues aredefined. Each packet queue is associated with a unique set oftransmission parameters. For example, the most robust queue could bedefined as using QPSK modulation with a FEC code rate of ½. This queuehas relatively low throughput but also requires a very low SNR receivedat the SM. The least robust queue could be defined with 16 QAMmodulation and a FEC code rate of ¾ for example. This queue has a muchhigher throughput, but also requires higher received SNR to achieve lowerror rate performance. Using this technique, a number of packet queuesare defined, each of which meets respective downstream signal qualityrequirements. The plurality of packet queues is spaced rationally acrossa range that corresponds to an expected operating range of the SMs inthe system.

[0023] The data traffic is assigned to a queue based on the downstreamsignal quality information for each of the subscribers. This informationis measured by each SM and transmitted back to the SG in the upstreamchannel. Downstream signal quality is periodically updated to reflectthe possibility of changing channel conditions for each subscriber.Knowledge of the downstream signal quality for each SM allows the SG toassign the traffic for each SM to the proper packet queue. Overallefficiency is maximized when traffic for each subscriber is placed inthe queue that has the highest throughput that can be supported by thedownstream signal quality of the SM in question. However, if necessarytraffic can be placed in or moved to a more robust packet queue andstill be received by the SM.

[0024] Data is extracted from each packet queue in queue blocks (QBs)that have a known size and duration. Each of these QBs must be modulatedwith the transmission parameters associated with the originating packetqueue. Each SM configures its demodulation parameters to receive the QBsthat its downstream signal quality allows it to receive. The SG mustcommunicate the data structure (i.e., the type, order and number of eachQB) to both the downstream modulator (at the SG) and the SM.

[0025] The SG communicates this information to the SM via a PHY-MAPcontrol message. This message must be receivable by all SMs, and mustspecify the parameters required to demodulate and decode the downstreamdata. At the SG, the modulator can use the PHY-MAP to set the requiredtransmission parameters for each QB, or other control information can begenerated and used.

[0026] In an adaptive modulator controller constructed according to thepresent invention, a DOCSIS MAC receives network data such as IP dataand produces a number of DOCSIS packets. These packets are placeddirectly into the packet queues, or framed into the traditional MPEGstream specified by the DOCSIS downstream transmission convergence layerspecification. If the MPEG stream is used, a parser extracts the DOCSISpackets and places them in a number of packet queues. Each packet queuerepresents particular throughput rate or bandwidth efficiency. The morebandwidth efficient, the less tolerant the transmission is of degradedsignal at the downstream receiver. The traffic is assigned to each ofthe receivers based on its current signal quality. Data is formed intoqueue blocks and each queue block is transmitted with the transmissionparameters assigned to the given queue. A PHY-MAP is transmitted in thedownstream data to give the SMs knowledge of the downstream datastructure. Each SM decodes the PHY-MAP and demodulates the queue blockswith transmission parameters appropriate for that queue block. Ingeneral, some SMs will be unable to decode certain queue blocks due todownstream signal quality requirements that are higher than that beexperienced by the given SM. The SG endeavors not to place traffic for agiven SM in a queue block that it cannot receive. It accomplishes thistask with knowledge of the downstream signal quality for each SM that isreported to it via the upstream channel.

[0027] Other features and advantages of the present invention willbecome apparent from the following detailed description of the inventionmade with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0028] The Downstream Adaptive Modulation (DS-AM) method and apparatusof the invention may be better understood, and its numerous objectives,features, and advantages made apparent to those skilled in the art byreferencing the accompanying drawings. The use of the same referencenumber throughout the several figures designates a like or similarelement.

[0029]FIG. 1 illustrates the basic elements of a two way satellite datasystem;

[0030]FIG. 2 is a block diagram illustrating the processing blocks of aknown satellite gateway (SG);

[0031]FIG. 3 is a block diagram illustrating the processing blocks of aknown satellite modem (SM);

[0032]FIG. 4 is a block diagram illustrating the processing blocks of anembodiment of a satellite gateway (SG) 100 b, that incorporates theDownstream Adaptive Modulation (DS-AM) method and apparatus of theinvention;

[0033]FIG. 5 illustrates a block diagram of the adaptive modulationformatter & controller (AMFC) of FIG. 4;

[0034]FIG. 6 is a block diagram illustrating the processing blocks of anembodiment of a satellite modem (SM), which incorporates the DS-AMmethod and apparatus of the invention.

[0035]FIG. 7 illustrates a queing example given a MPEG data stream inputto the AMFC.

[0036]FIG. 8 illustrates an example output the AMFC based on the profileestablished for the packet queue in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

[0037]FIG. 4 is a block diagram illustrating the processing blocks of anembodiment of a satellite gateway (SG) 100 b that incorporates theDownstream Adaptive Modulation (DS-AM) method and apparatus of theinvention. The SG 100 b includes an adaptive modulation and formattingand control (AMFC) stage 406 that receives and processes the DOCSISencapsulated traffic received from the MAC processing block 204 b.Interface 240 b could be a MPEG data stream compliant with the DOCSISdownstream transmission convergence sublayer, or it could have analternative format. The SG 100 b also includes a variable encoding &modulation stage 408, which is a modulator that is capable of having itsmodulation type and FEC encoding parameters dynamically controlled on aQB by QB basis.

[0038]FIG. 5 illustrates a block diagram of the AMFC block 406 of FIG.3. The host controller 200 b receives downstream signal qualityinformation for each of the particular SMs 112 b over the upstreamchannel. The SM 112 b is an embodiment of a satellite modem that isoperable to receive and decode downstream transmissions from the SG 100b that have been adaptively modulated and encoded using the DS-AM methodand apparatus of the invention. The SM 112 b will be discussed in moredetail below.

[0039] The downstream signal quality for each SM 112 b can be based on,for example, the SNR, packet or code word error rate, or otherparameters defining signal quality. The SM 112 b can be made to monitorthat information continuously, so that any changes in the signal qualitymay be dynamically reflected at the SG 100 b. Different sets oftransmission parameter profiles (including values for modulation type,FEC type and FEC rate) are defined spanning the range of expected signalquality. An example of a set of four profiles based on SNR as a signalquality measurement are shown below in Table 1. As Table 1 illustrates,the profiles trade-off higher throughput (shown as higher bandwidthefficiency in Table 1) for higher required signal quality. Clearly,Table 1 is only a hypothetical example. Other profiles with differentperformance characteristics and different transmission parameters couldbe specified while staying within the scope of the invention. TABLE 1Example Transmission Parameter Profiles for DS-AM BW Eff RequiredProfile Mod FEC Rate [bits/sec/Hz] SNR 1 QPSK 1/2 1.0 3.0 2 QPSK 3/4 1.56.0 3  8 PSK 2/3 2.0 9.0 4 16 QAM 3/4 3.0 12.0

[0040] The host controller 200 b assigns each of the different profilesto one or more of the queues 602. Put another way, each packet queue 602is associated with a unique modulation order and/or FEC code rate thatdefines a throughput rate in the form of bandwidth efficiency (i.e. bitsper second per 1 Hz of bandwidth. Traffic for a given SM 112 b is thenassigned to a specific queue or set of the queues 602 having an assignedprofile that is appropriate for the downstream quality informationprovided by that SM 112 b. Sufficient information is associated witheach packet to allow it to be assigned to the proper queue. For example,the packets can be assigned to the different queues 602 by means of theDOCSIS Destination Address (DA), Service ID (SID), or any other uniqueidentifier that is available with the DOCSIS protocol.

[0041] The adaptive modulation formatter & controller block 406 receivesthe data stream 240 b from the Gateway MAC 204 b. DOCSIS packetsdestined for individual SMs 112 b are parsed and placed in theirassigned packet queues 602. One possible format for the data interfacebetween the Gateway MAC 204 b and the AMFC 406 is an MPEG format. FIG. 7illustrates the DOCSIS packets of the data stream 240 b residing in aMPEG format. As shown, four DOCSIS packets are overlaid on the MPEGformat. Each MPEG frame has a length of 188 bytes. The example in FIG. 7shows as the first packet PHY-MAP and hence as input externally to theAMFC 406. In alternate implementations, the PHY-MAP could be generatedinternally in the AMFC 406. The parser 602 is able to extract the DOCSISpackets 702, 704, 706 and 708 from the MPEG stream, and based on theirDOCSIS destination addresses or other unique identifier rout them totheir assigned packet queues 602 a-602 n. In this case, it is assumedthat DOCSIS packets #1, 702 and #3 706 are assigned to packet queue 602a, while packet #2 704 is assigned to queue 602 b and #4 708 is assignedto the last packet queue 602 n.

[0042] The profiles for the various queues are defined by theirtransmission parameters. These parameters include, but are notnecessarily limited to: the modulation type, FEC type, FEC rate, FECblock size, and QB size (or equivalently number of MPEG frames per QB).The example in FIG. 7 illustrates profiles that are defined by QPSKmodulation with a rate ½ code (queue 602 a), 8-PSK modulation with arate ⅔ code (queue 602 b) and 16 QAM modulation with a rate ¾ code(queue 602 n). As discussed, the profile parameters are defined toaccommodate the system performance objectives and downstream signalquality requirements. They would ideally be based on traffic signalquality conditions experienced by the subscribers. In the example ofFIG. 7, queue 602 a has a profile that is typically used for a worstcase signal to noise ratio, as the order of the modulation type is lowand the error correction code rate is only one bit of two being payload,and every other bit being a parity bit. While the bandwidth efficiencyis quite low for this combination, it produces a very robusttransmission even in worst case signal conditions. The profile for Q #2is somewhat better in bandwidth efficiency, and is more suitable forreceivers or subscribers that are experiencing better SNR ratios. Theleast robust queue (queue 602 n) has the highest bandwidth efficiency,but also requires the highest downstream signal quality.

[0043] As previously discussed, a worst case queue guarantees thatDOCSIS MAC management type messages, or that the current configurationof the PHY-MAP has been received by all receivers. This is crucial forthe proper operation of SM 112 b receivers. They must all know how thedownstream data stream has been formatted at any given time for properdemodulation and decoding of the downstream data. There is an inherentcost/benefit trade-off in selecting the size of the queue blocks. LargeQ blocks tend to facilitate more efficient mapping of data packets andprovides the opportunity for more effective interleaving to spreaderrors. Shorter packets minimize latency and facilitate a more exactmatch between the traffic conditions and the proportion of capacityassigned to each queue.

[0044] This description of the downstream data structure (i.e. thenumber and type of each queue block transmitted) are stored in PHY-MAPs.The PHY-MAP spans a known time period and contains the informationnecessary for the SMs to determine the sequence of queue blocks arrivingin the downstream and hence to demodulate and decode each queue blockthat it is capable of receiving (i.e. the SM receives the queue blocksfor which it has the required downstream signal quality). The PHY-MAPcan also contain information that defines start times of bursts fromeach queue 602 to which each profile is assigned, and the duration inthe number of QBs. PHY-MAPs span a finite period of time and areinserted into the downstream and transmitted periodically Thus, therelative time allocated for transmission of each queue 602 can bedynamically changed in the PHY-MAPs to optimize overall systemthroughput and maximize efficiency. For example, if a very large rainstorm affects a large number of subscribers, the low throughput, morerobust queue may become full more quickly than the other queues.Similarly, if it is extremely clear and sunny, the higher through rate(i.e. higher bandwidth efficient) queues may become fuller faster. Inthis case, the controller 604 can sense this and increase the sizeand/or number of the QBs that define a burst from a queue. The structureof the PHY-MAP is not critical and can be determined by the hostprocessor 200 b, the embedded controller 604, or other external entitythat has knowledge of the traffic statistics, and signal qualitydistribution of the SMs 112 b.

[0045] The imbedded controller 604 provides control information to theMPEG Framer 608 based on the PHY-MAP profile information for each packetqueue 602, and packet data is thereby extracted from the packet queues602 and framed according to the profile definitions in the PHY-MAP.Modulation control can be achieved by sending the PHY-MAP to theVariable Encoding & Modulation block 408 of FIG. 4. Alternately, themodulation control could be a separate processing block that providesmodulation control information (as shown as 618 in FIG. 5). Regardlessof the specific implementation, modulation control must be provided tothe Variable Encoding & Modulation block 408 such that each queue blockis transmitted with the proper transmission parameters.

[0046]FIG. 8 illustrates an output 420 of MPEG framer 608 based on theprofile established for the queues 602 a, 602 b, and 602 c of FIG. 7.The output starts out with the PHY map message 702 destined for all ofthe receiver/subscribers (in this example, packet 702 is interpreted tobe the PHY-MAP). As shown, the PHY-MAP is included in a queue blockhaving the most robust transmission parameters. From information in thePHY-MAP, the SMs will know the map of the content of the downstream theyare receiving and therefore how to decode and demodulate it. Queueblocks are transmitted in accordance with the sequence defined by thePHY-MAP. In the example shown in FIG. 8, this sequence includes a QBfrom queue 602 a, a QB from queue 602 b, and a queue block from queue602 n. These QBs contain the example DOCSIS packets 704, 706 and 708.DOCSIS time stamps or other MAC messages would be included in queue 602a (the most robust queue). The QBs are provided to the variable encodingand modulation stage (408, FIG. 4) over output 420. The modulationcontrol signals can be embedded in 420, or implemented as a separateinterface 422 (or some combination of the two approaches).

[0047] As previously mentioned, any data transmitted for all SMs 112 bto receive must be processed through the packet queue 602 with the mostrobust profile (and therefore the lowest throughput to ensure that eventhe most degraded SMs 112 b are able to receive the messages. Thisincludes the PHY-MAP itself, which all SMs 112 b must receive andutilize to properly decode the downstream data. The SMs must know theprofiles for each frame of data coming in, so that it can adaptivelyapply the correct demodulation and error decoding to the received dataon a QB by QB basis. Other such messages that must be transmittedthrough the most robust queue 602 include all DOCSIS timestamps, DOCSISMAC management messages and all other multi-cast data.

[0048] As previously discussed, the SMs 112 b must be able to decode anddemodulate the adaptively modulated stream. FIG. 6 is a block diagramillustrating the processing blocks of an embodiment of a satellite modem(SM) 112 b, which incorporates the DS-AM method and apparatus of theinvention. The adaptive demodulation and decoding block 560 decodes thePHY-MAP message (702, FIG. 8) sent from the Gateway (SG 100 b). Thismessage is used to determine the proper demodulation and decodingparameters to use during the proper time intervals (i.e. for each QB).The SM 112 b always decodes and demodulates the most robust data packetqueue to extract the timestamp and MAC management messages sent to allSMs 112 b.

[0049] The SMs 112 b use the MAC management messages to set up anupstream channel to the GM 100 b. SM 112 b uses this upstream channel tosend downstream signal quality metrics to the host of the SG 100 b. Thiscould be implemented as part of the ranging and registration processcommon to these systems or as separate MAC messages. Based on its signalquality, each SM 112 b identifies the maximum downstream throughput ratethat it can handle with acceptable fidelity, and decodes data receivedfrom the packet queue assigned to handle that throughput rate as well asfrom any queue having a more robust profile. If any packet queue cannotbe demodulated by the SM 112 b with appropriate fidelity, the SM 112 bfills output MPEG frames corresponding to that queue with null MPEGframes, or otherwise blanks the data sent to the SM DOCSIS MAC 504 b.The decoded stream is transmitted to the SM DOCISIS MAC 540 b overoutput 520 b.

[0050] The Gateway SG 100 b uses the PHY-MAP for flexible and optimizedassignment of QBs to the downstream. As channel conditions or trafficloading changes, the PHY-MAP can be dynamically adjusted to optimizeefficiency. Decoding all possible queues by the SM 112 b assures thatall SMs 112 b will receive PHY-MAP messages and multi-cast traffic overthe packet queue having the most robust modulation and encoding. It alsopermits Gateway SG 100 b the flexibility to assign traffic destined fora given SM 112 b to the queue having the highest possible throughput, orto any of the more robust queues.

[0051] Those of average skill in the art will recognize that the DS-AMof the invention can be achieved in the time or frequency domain. Whileembodiments disclosed herein are time domain implementations, it iscontemplated that the principals of the invention as disclosed may beextended to the frequency domain without exceeding the intended scope ofthe invention. Moreover, those of average skill in the art willrecognize although the embodiments disclosed herein within the contextof DOCSIS based satellite systems, the method and apparatus of theinvention may easily be applied to other types of DOCSIS data systems,such as terrestrial fixed wireless systems and cable modem systems.

[0052] The invention disclosed herein is susceptible to variousmodifications and alternative forms. Specific embodiments therefore havebeen shown by way of example in the drawings and detailed description.It should be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the invention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the claims.

What is claimed is:
 1. A method of adaptively controlling the throughputrate of data traffic destined for each of a plurality of receivers, thedata traffic combined into a single data stream and transmitted over asingle downstream channel, said method comprising: assigning datatraffic for each of the receivers to a throughput rate based ondownstream signal quality information for each of the receivers;associating each of a plurality of packet queues with one of theplurality of throughput rates, establishing a plurality of profiles foreach of the packet queues, each of the profiles comprising a modulationtype and an error correction encoding rate that supports the throughputrate; parsing the data stream into the plurality of packet queues basedon said assigning; modulating and encoding the parsed data traffic ineach of the packet queues in accordance with the associated profile; andtransmitting the modulated and encoded data traffic from each of thepacket queues over the downstream channel.
 2. The method of claim 1wherein the signal quality information is the signal-to-noise ratio forthe receiver.
 3. The method of claim 1 wherein the signal qualityinformation is the packet error rate for the receiver.
 4. The method ofclaim 1 further comprising receiving the signal quality information fromeach of the plurality of receivers over an upstream signal channel. 5.The method of claim 1 wherein said assigning further comprises placing apacket queue identifier in each traffic packet of the data stream. 6.The method of claim 1 wherein said assigning further comprises assigningthe data traffic destined for one of the plurality of receivers to anyone or more throughput rates that are supported by the signal qualityinformation of the receiver.
 7. The method of claim 1 wherein thedescription of the downstream data structure are stored in PHY-MAPs,said method further comprising transmitting the PHY-MAPs to each of thereceivers over the downstream channel, wherein the description of thedownstream data structure includes all information necessary for theplurality of receivers to demodulate and decode the modulated andencoded data traffic.
 8. The method of claim 7 wherein said transmittingthe PHY-MAP further comprises assigning the PHY-MAP to the lowestthroughput rate.
 9. The method of claim 1 further comprising: generatingthe data stream in accordance with a DOCSIS MAC layer, and assigningDOCSIS MAC management messages and DOCSIS time stamp messages to thelowest throughput rate.
 10. The method of claim 9 further comprising:extracting packet data from the packet queues; and framing the extractedpackets in accordance with the profile stored in the PHY_MAP for eachqueue from which the data is extracted and framed.
 11. The method ofclaim 10 wherein said modulating and encoding further comprisesgenerating modulation and encoding control signals for each burst from aqueue in accordance with the profile associated with the queue fromwhich the framed data was extracted.
 12. The method of claim 11 furthercomprising updating the PHY-MAP periodically to reflect changingdownstream signal quality information.
 13. The method of claim 1 whereinthe profile for each packet queue includes information selected from thegroup consisting of modulation type, FEC type, FEC rate, FEC block size,queue block size, and a number of MPEG frames per queue block.
 14. Themethod of claim 13 further comprising dynamically allocating time fortransmission from each queue to optimize overall system throughput byaltering the number of blocks and the number of MPEG frames per block.15. A method for adaptively modulating data traffic comprising a datastream, said method comprising: parsing the data stream into a pluralityof packet queues; establishing a plurality of profiles for each of thepacket queues, each of the profiles comprising a modulation type and anerror correction encoding rate; extracting packet data from the packetqueues; framing the extracted packets in accordance with the profileassociated with the queue from which the packet is extracted; andmodulating and encoding the parsed data traffic in each of the packetqueues in accordance with the associated profile.
 16. An apparatus foradaptively controlling the throughput rate of data traffic destined foreach of a plurality of receivers, the data traffic combined into asingle data stream and transmitted over a single downstream channel,said apparatus comprising: means for assigning data traffic for each ofthe receivers to a throughput rate based on downstream signal qualityinformation for each of the receivers; means for associating each of aplurality of packet queues with one of the plurality of throughputrates, means for establishing a plurality of profiles for each of thepacket queues, each of the profiles comprising a modulation order and anerror correction encoding rate that supports the throughput rate; meansfor parsing the data stream into the plurality of packet queues based onsaid assigning; means for modulating and encoding the parsed datatraffic in each of the packet queues in accordance with the associatedprofile; and means for transmitting the modulated and encoded datatraffic from each of the packet queues over the downstream channel. 17.The apparatus of claim 16 wherein the signal quality information is thesignal-to-noise ratio for the receiver.
 18. The apparatus of claim 16wherein the signal quality information is the packet error rate for thereceiver.
 19. The apparatus of claim 16 further comprising means forreceiving the signal quality information from each of the plurality ofreceivers over an upstream signal channel.
 20. The apparatus of claim 16wherein said means for assigning further comprises means for placing apacket queue identifier in each traffic packet of the data stream. 21.The apparatus of claim 16 wherein said means for assigning furthercomprises means for assigning the data traffic destined for one of theplurality of receivers to any one or more throughput rates that aresupported by the signal quality information of the receiver.
 22. Theapparatus of claim 16 wherein the associated profiles are stored in aPHY-MAP, said apparatus further comprising means for transmitting thePHY-MAP to each of the receivers over the downstream channel.
 23. Theapparatus of claim 22 wherein said means for transmitting the PHY-MAPfurther comprises means for assigning the PHY-MAP to the lowestthroughput rate.
 24. The apparatus of claim 16 further comprising: meansfor generating the data stream in accordance with a DOCSIS MAC layer,and means for assigning DOCSIS MAC management messages and DOCSIS timestamp messages to the lowest throughput rate.
 25. The apparatus of claim16 further comprising: means for extracting packet data from the packetqueues; and means for framing the extracted packets in accordance withthe profile stored in the PHY_MAP for each queue from which the data isextracted and framed.
 26. The apparatus of claim 25 wherein said meansfor modulating and encoding further comprises means for generatingmodulation and encoding control signals for each frame in accordancewith the profile associated with the queue from which the framed datawas extracted.
 27. The apparatus of claim 26 further comprising meansfor updating the PHY-MAP based on periodically to reflect changingdownstream signal quality information.
 28. The apparatus of claim 16wherein the profile for each packet queue further comprises start timesfor bursts from each queue.
 29. The apparatus of claim 28 furthercomprising means for dynamically allocating time for transmission fromeach queue to optimize overall system throughput.
 30. An apparatus foradaptively modulating data traffic comprising a data stream, saidapparatus comprising: means for parsing the data stream into a pluralityof packet queues; means for establishing a plurality of profiles foreach of the packet queues, each of the profiles comprising a modulationorder and an error correction encoding rate; means for extracting packetdata from the packet queues; means for framing the extracted packets inaccordance with the profile associated with the queue from which thepacket is extracted; and means for modulating and encoding the parseddata traffic in each of the packet queues in accordance with theassociated profile.